T3 (Triiodothyronine), Total                 Reference Range(s)

T4 (Thyroxine), Total

4.5-12.0 mcg/dL

Thyroid Stimulating Hormone (TSH)               Reference Range(s)

Table 1. Interpretation of the Thyroid Profile Test results

TSH	T4	T3	INTERPRETATION
Elevated	Normal	Normal	Mild (subclinical) hypothyroidism
Elevated	Low	Low or normal	Hypothyroidism
Low	Normal	Normal	Mild (subclinical) hyperthyroidism
Low	Elevated or normal	High or normal	Hyperthyroidism
Low	Low or normal	Low or normal	Nonthyroidal illness; hypothyroidism due to the disease involving the pituitary gland
Normal	Elevated	Elevated	Thyroid hormone resistance (Impaired sensitivity to thyroid hormone)

• Low T4 and T3 along with high TSH level indicates hypothyroidism. The most common cause of hypothyroidism is Hashimoto thyroiditis 
• High T4 and T3 along with low TSH indicate hyperthyroidism. The most common cause of hyperthyroidism is Graves disease
• Normal thyroxine (T4) and T3 along with high TSH usually indicates mild or subclinical hypothyroidism 
• Normal T3 and T4 along with low TSH indicates mild or subclinical hyperthyroidism 

Note: TSH levels show circadian variation (fluctuates during the 24-hour cycle), reaching peak levels between 2 - 4 am and are at a low between 6-10 pm.

Reference Range(s) may vary from lab to lab.

The thyroid gland (a small, butterfly-shaped gland located in front of the neck) secretes the following hormones:

• Triiodothyronine (T3)

• Thyroxine (T4)

Thyroid Stimulating Hormone (TSH), also called Thyrotropin is a hormone secreted into the blood by a gland present in the brain (Pituitary gland) and it tells your thyroid gland to make and release the thyroid hormones (T3 & T4) into your blood. The thyroid gland uses iodine from food to make the thyroid hormones.

The thyroid hormones are essential for growth and metabolism. If the thyroid gland produces very high amounts of these hormones (T3 and T4), you may experience symptoms of weight loss, rapid heartbeat, tremors, sweating, anxiety, increased sensitivity to heat etc. and this is known as Hyperthyroidism.

Also, the decreased production of thyroid hormones (T3 and T4) results in Hypothyroidism which may cause symptoms like weight gain, fatigue, slow heart rate, increased sensitivity to cold, depression, dry and thin hair etc.

There is a feedback system in the body to maintain stable amounts of the thyroid hormones (T3 and T4) in the blood. When thyroid hormone levels decrease, the pituitary gland is stimulated to release TSH. This high TSH in turn leads to the release of more thyroid hormones (T3 & T4) from the thyroid gland and vice-versa.

T3 and T4 circulate in the blood in two forms:

1) Bound form - It is bound to proteins present in blood and this prevents it from entering body tissues. The three main proteins in the blood that the thyroid hormones are bound to are albumin, transthyretin and Thyroxine-binding globulin (TBG), also called Thyroid hormone Binding Globulin (THBG).

2) Free form - It enters the body tissues where it's needed

The total T3 or total T4 includes both bound and free forms circulating in the blood. Hence, thyroid hormones can be measured as Free T3, Total T3, Free T4 and Total T4.

The total T3 and total T4 levels can be affected by the amount of protein available in the blood to bind to them.

Hyperthyroidism is a condition in which the thyroid gland is overactive and there is an increased production of thyroid hormones by the thyroid gland. Causes of Hyperthyroidism include Graves disease, multinodular goiter, thyroid nodules, toxic adenoma, inflammation of the thyroid, eating too much iodine, and too much synthetic thyroid hormone. Diagnosis of this condition can help to relieve the symptoms and prevent long term complications.

Symptoms of Hyperthyroidism include: n nRapid heartbeat (tachycardia) commonly more than 100 beats/minute irregular heartbeat (arrhythmia) or pounding of your heart (palpitations), sudden weight loss, nnervousness, anxiety, irritability, tremor (usually a fine trembling in your hands and fingers), nchanges in menstrual patterns, increased sensitivity to heat, changes in bowel patterns (especially more frequent bowel movements), nan enlarged thyroid gland (goiter) which may appear as a swelling at the base of your neck, increased appetite, sweating, fatigue, muscle weakness, sleep disturbances, skin thinning, fine and brittle hair

Hypothyroidism, also called underactive thyroid or low thyroid is a condition in which the thyroid gland does not produce enough thyroid hormones. It can be commonly caused by intake of low iodine diet or Hashimoto's thyroiditis (an autoimmune disease). Less common causes include previous treatment with radioactive iodine, injury to the pituitary gland which secretes TSH, intake of certain medicines, previous thyroid surgery or a lack of a functioning thyroid gland at birth.

Symptoms of Hypothyroidism include:nTiredness (fatigue), constipation, feeling cold, dry skin, weight gain, muscle weakness, decreased sweating, depression, slowed heart rate, increased blood cholesterol levels, pain and stiffness in your joints, impaired memory, problems of infertility or menstrual changes, muscle stiffness, aches, and tenderness, hoarseness, puffy face, dry and thin hair

This test is performed on a blood sample. A syringe with a fine needle attached is used to withdraw blood sample from a blood vessel in your arm generally from the inner side of the elbow area. The doctor, nurse or the phlebotomist will tie an elastic band around your arm which will help the blood vessels to swell with blood and hence makes it easier to withdraw blood. You may be asked to tightly clench your fist. Once the veins are clearly visible, the area is cleaned with an antiseptic solution and then the needle is inserted into the blood vessel to collect the sample. You may feel a tiny pinprick during the procedure. Blood sample once collected is then sent to the laboratory.

There is no risk associated with the test. However, as this test involves a needle prick to withdraw the blood sample, rarely, a patient may experience increased bleeding, hematoma (blood collection under the skin) formation, bruising or infection at the site of needle prick.

An untreated hyperthyroidism during pregnancy can lead to miscarriage, premature birth, low birth weight, preeclampsia (a very high rise in blood pressure in late pregnancy), thyroid storm (a sudden, severe worsening of symptoms of hyperthyroidism) and congestive heart failure.

An untreated hypothyroidism during pregnancy can cause preeclampsia (a very high rise in blood pressure in late pregnancy), anemia, miscarriage, low birthweight, stillbirth (death or loss of a baby before or during delivery) and rarely congestive heart failure. These problems occur most often with severe hypothyroidism.nAs the thyroid hormones play an important role in the development of babys brain and nervous system, untreated hypothyroidismespecially during the first trimestercan cause low IQ and other problems with normal development.

Congenital hypothyroidism is an important cause of elevated thyroid-stimulating hormone (TSH) in newborns. Other causes of an elevated TSH include transient hypothyroidism due to neonatal illness, premature birth, iodine excess or deficiency. High TSH can also be seen in case the mother is taking some medicines that could affect thyroid hormone levels or the mother has some underlying thyroid disease.

Inform the doctor about any medications you may be taking. No other specific preparations are usually required before this test.

If the thyroid profile total test results are not in the normal range, your doctor may ask for the following tests: Thyroid Hormone Binding Globulin (THBG), Thyroid profile Free, Anti Thyroperoxidase Antibody test.